The objectives are to ascertain the structural basis of nephron filtration in normal and nephrotic animals models. To achieve these objectives, an array of ultrastructural, fluorescent and radiographic macromolecular tracers will be employed to ascertain the pathways and structural barriers of glomerular and tubular filtration in hopes that an understanding of proteinuria in human renal disease will be forthcoming. In addition, scanning and cytochemical studies will be utilized to elucidate glomerular morphology and study the histochemistry of the glomerular tuft, respectively.